The term “malware” is short for malicious software and is used as a term to refer to any software designed to infiltrate or damage a computer system without the owner's informed consent. Malware can include viruses, worms, trojan horses, rootkits, adware, spyware and any other malicious and unwanted software. Any computer device, such as a desktop personal computer (PC), laptop, personal data assistant (PDA) or mobile phone, can be at risk from malware.
When a device is infected by malware the user will often notice unwanted behaviour and degradation of system performance as the infection can create unwanted processor activity, memory usage, and network traffic. This can also cause stability issues leading to application or system-wide crashes. The user of an infected device may incorrectly assume that poor performance is a result of software flaws or hardware problems, taking inappropriate remedial action, when the actual cause is a malware infection of which they are unaware.
Computer devices make use of anti-virus software to detect and possibly remove malware. This anti-virus software can make use of various methods to detect malware including scanning data on the computer. Malware scanning generally involves examining files for a virus fingerprint or “signature” that is characteristic of an individual malware program.
Malware scanning can require a large amount of processor time as large quantities of data generally needs to be checked each time a malware scan is carried out. Some anti-virus software therefore stores a hash for each file that is scanned and identified as not containing any malware. When a file that has previously been scanned and identified as not containing any malware is subsequently checked for malware by the anti-virus software, a corresponding hash can be generated from the file and checked against stored hashes. If a stored hash and newly generated hash match then the file has not been modified and since it was previously scanned and identified as not containing any malware it is determined that the file still does not contain any malware and full scanning is not carried out.